Among engines mounted on vehicles and the like, there is one type of engine in which a cylinder block has a plurality of cylinders aligned with one another. A plurality of spark plugs are serially arranged in a row within a cylinder head positioned above the cylinders. There is another type of engine in which the cylinder head has a head cover mounted thereon for covering a valve-actuating mechanism such as a cam shaft.
FIGS. 13 through 15 illustrate a head cover structure mounted on a cylinder head of an engine in which a plurality of spark plugs are fitted in the cylinder head, as described above. In these figures, the head cover 102 is mounted on an engine cylinder head (not shown).
In the engine, a cylinder block has a plurality of cylinders (not shown) aligned with one another. While being located above the plurality of cylinders, the plurality of spark plugs (not shown) are placed at a central portion of the cylinder head in a transverse direction perpendicular to axis C of a crank shaft (not shown). The plurality of spark plugs are arranged in a row in series along a longitudinal direction parallel to axis C.
In addition, the engine is not provided with a distributor, but is provided with a so-called distributorless ignition (DLI) in which an ignition coil is provided for each of the cylinders. The ignition coils are mounted directly onto head portions of the spark plugs which are fitted in the cylinder head.
The cylinder head has the head cover 102 mounted thereon for covering a valve-actuating mechanism such as a cam shaft. The head cover 102 is formed by a peripheral platelike flange portion 104 and an upper plate portion 106. The peripheral flange portion 104 forms the periphery of the head cover 102. The upper plate portion 106 is surrounded by the peripheral flange portion 104. The upper plate portion 106 is dented inwardly to provide an elongated groove 108, whereby the head cover 102 has the upper plate portion 106 defined with the elongated groove 108 therein. The elongated groove 108 is provided by the denting of a central portion of the upper plate portion 106 in the transverse direction perpendicular to axis C in such a manner that the elongated groove 108 is located at a position corresponding to locations where the plurality of spark plugs are fitted in the cylinder head. The above denting is conducted to a stage where the elongated groove 108 terminates at the peripheral flange portion 104 at least at one end of the upper plate portion 106 in the longitudinal direction parallel to crank shaft axis C.
The elongated groove 108 is formed by a bottom plate portion 110 and side plate portions 112, the latter being located at both sides of the former. The bottom plate portion 110 is formed with a plurality of spark plug insertion-through-portions 114, through which the plurality of spark plugs are individually inserted. The spark plug insertion-through-portions 114 are provided through the bottom plate portion 110 at respective positions corresponding to the locations where the spark plugs are fitted in the cylinder head. Further, the spark plug insertion-through-portions 114 are defined with spark plug insertion holes 116. When water or the like lodges in the elongated groove 108 around the spark plug insertion-through-portions 114, such is caused to flow to the open end of the elongated groove 108 in the longitudinal direction parallel to axis C. The water is then discharged outside.
The bottom plate portion 110 is further formed with coil-mounting portions 120 for ignition coils 118 (FIG. 15) which are mounted onto the spark plugs. Each of the coil-mounting portions 120 has a cylindrical shape, and is supported by supporting ribs 122. The coil-mounting portions 120 are positioned on both sides of the spark plug insertion-through-portions 114 in the longitudinal direction parallel to axis C. The coil-mounting portions 120 are provided on the bottom plate portion 110, and are disposed on opposite sides of the respective portion 114, to define a cooperative pair. Each ignition coil 118 is mounted onto a cooperative pair of coil-mounting portions 120 by mounting screws 126 threadingly engaged with coil-mounted holes 124 formed in the coil-mounting portions 120.
Moreover, the head cover 102 has bleeder chambers 128 (FIG. 14) formed on both sides of the elongated groove 108 in the transverse direction perpendicular to axis C. Through the raising of the peripheral flange 104 of the head cover 102 and the upper plate portion 106 on both sides of the elongated groove 108, the bleeder chambers 128 are defined by the peripheral flange portion 104, the upper plate portion 106, the side plate portions 112 of the elongated groove 108, and a bleeder plate 130.
One example of the above-described head cover structure is disclosed in Japanese Utility Model Application Examined No. 63-37461 (1988). According to the head cover disclosed in this publication, first and second chambers for separating oil from blow-by gases are provided within the head cover. The first and second chambers are spaced apart from each other by a predetermined gap. The first chamber is interposed in a first blow-by passageway that intercommunicates the interior of the head cover and an air intake passageway on an upstream side of a throttle valve. The second chamber is located in a second blow-by passageway that intercommunicates the interior of the head cover and the air intake passageway at a downstream side of the throttle valve. Further, there is provided an opening for introducing blow-up gases from a space defined by the gap between the first and second chambers. The opening is formed at a side wall portion of at least one of the first and second chambers.
A head cover 102 as shown in FIGS. 13 through 15 is formed with an elongated groove 108 having an invariable cross-sectional shape. The elongated groove 108 extends continuously along a longitudinal direction parallel to axis C. This configuration has a problem of being incapable of ensuring a sufficient capacity of the bleeder chambers 128. As a result, there are inconveniences in that the bleeder chambers 128 have a reduced capacity, and the performance of separating oil from blow-by gases cannot be enhanced, thereby increasing oil consumption.
In the conventional head cover 102, coil-mounting portions 120 for the ignition coils 118 are formed on a bottom plate portion 110 in the elongated groove 108. For this reason, the coil-mounting portions 120 must be formed into a cylindrical shape. However, these cylindrical-shaped components create another problem in that the head cover 102 is deficient in self-supporting rigidity. Accordingly, there are inconveniences in that it is necessary to form supporting ribs 122 for increasing the self-supporting rigidity of the coil-mounting portions 120, thereby increasing the weight of the head cover 102.
As mentioned above, the conventional head cover 102 is formed with the elongated groove 108 having the invariable cross-sectional shape. More specifically, the bottom plate portion 110 of the elongated groove 108 as well as the side plate portions 112 on both sides of the bottom plate portion 110 are formed into a planar plate shape. This configuration causes problems in that the head cover 102 fails to ensure sufficient strength, and tends to resonate with noise and/or vibration resulting from engine actuation. As a result, there are inconveniences in which the rigidity of the head cover 102 is impaired, and noise emission and vibration caused by engine actuation are difficult to control.
In order to obviate the above-described inconveniences, the present invention provides a structure of a head cover mounted on a cylinder head of an engine in which a plurality of spark plugs are disposed at a central portion of the cylinder head in a transverse direction perpendicular to an axis of a crank shaft, the plurality of spark plugs being aligned with one another in a longitudinal direction parallel to the axis of the crank shaft, the structure of the head cover being characterized in that: an upper plate portion of the head cover is dented at respective regions corresponding to locations where the plurality of spark plugs are fitted in the cylinder head, whereby the head cover has the upper plate portion formed with dented grooves; the dented grooves have bottom plate portions defined with spark plug insertion-through-portions, through which the plurality of spark plugs are inserted; the upper plate portion has coil-mounting portions formed on both sides of the spark plug insertion-through-portions in the longitudinal direction parallel to the axis of the crank shaft, the coil-mounting portions being provided for mounting ignition coils directly onto the plurality of spark plugs; one of both sides of the upper plate portion, which is defined with the coil-mounting portions, in the transverse direction perpendicular to the axis of the crank shaft is dented to provide communication grooves which intercommunicate the dented grooves, the communication grooves terminating at a peripheral flange portion of the head cover at one of the ends of the head cover in the longitudinal direction parallel to the axis of the crank shaft, whereby the head cover has the upper plate portion formed with the communication grooves; and the head cover has bleeder chambers formed inside the upper plate portion that is defined with the coil-mounting portions, the bleeder chambers being positioned on the other side of the upper plate portion in the transverse direction perpendicular to the axis of the crank shaft.
According to the present invention having the aforesaid structure, an upper plate portion is dented at respective regions corresponding to locations where a plurality of spark plugs are fitted in a cylinder head, whereby a head cover has the upper plate portion formed with dented grooves. Further, the upper plate portion is dented to provide communication grooves which intercommunicate the dented grooves. The communication grooves terminate at a peripheral plate portion of the head cover. The head cover thereby has the upper plate portion formed with the communication grooves. As a result, the head cover is configured to have different groove shapes in cross-section. This configuration can increase the strength of the head cover without adding to the weight thereof.
Furthermore, in the head cover, the upper plate portion has a coil-mounting portion formed on each side of a spark plug insertion-through-portion in the longitudinal direction parallel to the axis of a crank shaft. The coil-mounting portions are provided for mounting ignition coils directly onto the spark plugs. This structure eliminates the need for conventional cylindrical-shaped coil-mounting portions. Accordingly, this feature can eliminate supporting ribs for enhancing the self-supporting rigidity of the coil-mounting portions.
Moreover, denting is made to one of the sides of the upper plate portion, which is defined with the coil-mounting portions, in a transverse direction perpendicular to the axis of the crank shaft. The head cover thereby has the upper plate portion formed with the communication grooves. The communication grooves intercommunicate the dented grooves, and terminate at the peripheral flange portion of the head cover. The head cover further has bleeder chambers formed inside the upper plate portion that is defined with the coil-mounting portions. The bleeder chambers are positioned on the other side of the upper plate portion in the transverse direction perpendicular to the axis of the crank shaft. This construction allows for an increased capacity of the bleeder chambers.